NAND Flash memory has become the preferred nonvolatile choice for portable consumer electronic devices. Features such as high density, low cost, and fast write times make NAND perfectly suited for media applications where large files of sequential data need to be loaded into the memory quickly and repeatedly. When compared to a hard disk drive, a limitation of the Flash memory is the finite number of erase/write cycles: most of commercially available NAND products are guaranteed to withstand 105programming cycles at most. As a consequence, special care (remapping, bad block management algorithms, etc.) has to be taken when hard-drive based, read/write intensive applications, such as operating systems, are migrated to Flash-memory based devices. One of the basic requirements of the consumer market for data storage is the portability of stored data from one device to the other. Flash cards are the actual solution. A Flash card is a nonvolatile ldquosystem in packagerdquo in which a NAND Flash memory is embedded with a dedicated controller. This paper presents the basic features of the NAND Flash memory and the basic architecture of Flash cards. We provide an outlook on opportunities and challenges of future Flash systems.

In the past few years, the complexity of logic functions and architectures inside a flash memory device has grown in order to face the need for more complex system interfaces and to manage the increased amount of stored data. In this paper, an overview of these developments will be given. The paper is divided into sections describing areas where logic circuits play a key role: program/erase algorithms handling and user interface, redundancy management for yield enhancement, error correction codes to enhance reliability, and burst and page mode access control to enhance read bandwidth.